Solid-state electrochemical devices are normally cells that include two porous electrodes, the anode and the cathode, and a dense solid electrolyte membrane disposed between the electrodes. In the case of a typical solid oxide fuel cell, the anode is exposed to fuel and the cathode is exposed to an oxidant in separate closed systems to avoid any mixing of the fuel and oxidants.
External seals are used to seal off the closed systems and prevent mixing. While no dominant seal technology exists, examples includes braze seals, compressive seals and glass seals. Seal-less designs, which allow mixing of the fuel and oxidant streams at the outlet of the device, have also been in development, though oxidant and fuel mixing is generally undesirable. Long-term performance of braze seals has not been demonstrated. In addition, braze seals can be costly and the coefficient of thermal expansion (“CTE”) must be modified to match the CTE of the electrolyte. Compressive seals are generally made with mica, display high leak rate and have poor thermal cycling capability. Glass seals can react with sealed surfaces and also have poor thermal cycling ability.